[LM93]

Going to look at a 350 block from a gentleman from here(400s are kinda rare west of the Mississippi). He has a set of 670 heads as well. I don't have much firsthand experience with Pontiacs. How well would those heads work with a 350? Is there something in particular to look out for for those older heads? Is there an at-a-glance way to tell what work needs to get done on them?

[blueghoast]

Originally Posted by LM93

Going to look at a 350 block from a gentleman from here(400s are kinda rare west of the Mississippi). He has a set of 670 heads as well. I don't have much firsthand experience with Pontiacs. How well would those heads work with a 350? Is there something in particular to look out for for those older heads? Is there an at-a-glance way to tell what work needs to get done on them?

check bore to valve clearance for the lift you'll be running.

GT

[steve25]

Well even before wondering what work the heads may need, please consider this.
1)
Stock 350 pistons basically have no valve notches so if you have plans of running a cam of over .450” lift that may be an issue.
2)
What year car is this 350 in. Because accessory brackets use in a 71 and up car may not bolt right up without a adapter.

In terms of the heads they need to pass a mag test to find if there cracked.

670s do not have a habit of cracking unless they have been very overheated.

Look at the chambers for sunken valves.

They should all stand proud of the chamber floor.

If a lot of them are sunken then the labor to replace even 4 of then can add 200 bucks to the cost of rebuilding them.

[Squidward]

High compression 400 heads are in general a pretty good fit for a 350 build, but with all the factors previously mentioned, very importantly valve lift clearance. It's real. I am running 400 heads on a 350 now.

670 heads usually demand a premium. They are also closed chamber. I would rather use high compression heads that are open chamber, which started (I think) with 061 heads from 1967, and other heads from 68-70.

It's a shame. 350's were scorned years ago as not worth building, and too many found their way to the scrap heap.

[sdbob]

I built 1 350 for my 65 a body,I liked it, used 6x heads off 350. I got a 75 350 block from dealer.it was out of a new Lemans I think,leaked near one of the freeze plugs that's why it was replaced. When I moved 26 yrs ago it went to scrap I hated too just couldnt take everything.

[LM93]

"670 heads usually demand a premium. They are also closed chamber. I would rather use high compression heads that are open chamber, which started (I think) with 061 heads from 1967, and other heads from 68-70."


Do the closed chambers's valve location not work well with the smaller bores? https://forums.maxperformanceinc.com...7&d=1610800822

I've read conflicting forum posts about detonation, are closed chambers more detonation prone or are they just usually high comp chambers to begin with?

[steve25]

The closed chamber heads are less likely to detonate per a given ratio.

[unruhjonny]

I would think this is essentially #48(1969) heads that were used on the 1969-350HO;
ensure clearance for valves;
IIRC those 1969-350HO short blocks had valve reliefs in the pistons, and notches at the tops of the bores for intake valve clearance.

The large valve "72cc" D-port heads were essentially carried over for four model years with small changes (including id numbers);
1967 = 670
1968 = 31
1968 = 16*
1969 = 48
1970 = 12

* = I could be mistaken, these may have been more akin to 80cc like the 1969 #62 and 1970 #13 castings

[LM93]

Originally Posted by Squidward

High compression 400 heads are in general a pretty good fit for a 350 build, but with all the factors previously mentioned, very importantly valve lift clearance. It's real. I am running 400 heads on a 350 now.

670 heads usually demand a premium. They are also closed chamber. I would rather use high compression heads that are open chamber, which started (I think) with 061 heads from 1967, and other heads from 68-70.

It's a shame. 350's were scorned years ago as not worth building, and too many found their way to the scrap heap.

So I would be better off getting a set of 72cc wedge chambers with small valves? I've read a lot of opinions about using alum heads on 350s, low rpm power comes up a lot. Street use mainly, maybe a track day here and there.

[steve25]

Please give us details as to what year this 350 is and if it’s stock or rebuilt and if the owner still has its original heads?
Depending on these details you might be better off with a set of heads like the 17s, 18s, the 1969 45s or 46s or the 1970 11s or the small valve number 16s.

The one down side to all of these casting numbers is that they all have only pressed in rocker studs which will limit the valve lift and secondarily the spring pressure you can run.

[LM93]

It's a bare '69 block. No original heads but it's a YE block, 265hp. Stock heads would be low on the compression side I'd assume. Up here in the Pacific Northwest vintage parts aren't as available as back east so even though a 400 is better all around so I'll take what I can get. I snagged a full set of TRW L2339 0.030 pistons off ebay a little while back, before I knew the first 350 block I had was cracked out. Wasn't planning on going the stroker route. Pulling press in studs and installing heli coils is in my skill range so no worries there. I have a pair of #47 heads, I measured them to be 80cc's.

[steve25]

Looks to me like with a .020” deck , your 80 CC heads and a 9.4 CC head gasket and those pistons that you will have a 9 to 1 compression ratio.

Mill your heads .045” and you will pretty much be at 9.5.

It’s better to drill and just tap for the new rocker studs that are 1/2” on the bottom.

It’s best to have a shop do this unless you have a good drill press that can handle a 1/2” bit and do the taping also.

You will need to make a wood 14 degree wedge to set the head on.

[grandam1979]

The 47 heads are listed by Pontiac as 72cc I’m surprised they checked 80cc they are usually a little closer to 72cc. I have a complete 69 350 with the 47 heads if I get a chance over the weekend I might check them. Unfortunately 350 engines are scrapped more than they are saved I have had this one for sale for a couple years for $200 and can’t move it or had any interest at all in it but can’t bring myself to scrap it either.

[steve25]

The 1969 cast 47 head gave a factory listed 9.2 comp on a 350,.
In reality its was lucky to be even 8.8 comp, so there’s no way they could check in at 72 CCs .
They would have had to have been milled .048” to go from 80CCs to 72.

If you do re-check your CC results keep this in mind if you have a good solid way to measure the chamber depths.

CC a chamber in each head and measure the depth at a repeatable spot.
Then measure the depth of all the other chambers , if the depth of each chamber is .003” or less then all the chamber volumes will be within .06 CC .

This is the super nice thing about the accuracy of Pontiacs machined chambers!

[Squidward]

Originally Posted by steve25

Looks to me like with a .020” deck , your 80 CC heads and a 9.4 CC head gasket and those pistons that you will have a 9 to 1 compression ratio.

Mill your heads .045” and you will pretty much be at 9.5.

It’s better to drill and just tap for the new rocker studs that are 1/2” on the bottom.

It’s best to have a shop do this unless you have a good drill press that can handle a 1/2” bit and do the taping also.

You will need to make a wood 14 degree wedge to set the head on.

It has been a while. But I have tapped a set of 47 heads, currently on my Lemans, for 1/2 base threads. It didn't require a drill press. But I did make a block to assist both as a stud puller and as a tap guide. Maybe I can find that thread.

[Squidward]

https://forums.maxperformanceinc.com...d.php?t=734861

Found it. 290-7201 studs, trimmed about 1/8" off the bottom. No drill required, just tap for 1/2-13. I used a steel block as a guide. Details in thread.

I guess it all depends on OP's performance needs.

I've done the helicoil thing before, didn't care as much for it.

47 heads seemed to be super plentiful for a while. 1970 11's are also decent medium compression 350 heads.